Cornejo, Leonardo

Abstract [en]

The main purpose of this thesis is to compare measured and calculated transfer functions. By doing so the accuracy of prediction in the numerical method and model is evaluated. Software utilizing the Boundary Element Method was used in order to calculate the sound propagation around a truck. Initially a control measurement and its corresponding calculation were performed in order to validate the intended methodology. The results from these confirmed that the software was able to produce results similar to the ones attained from the measurements. A series of measurements were made on a SCANIA truck in an anechoic room. The source was a dodecahedron that was moved around four stationary microphones positions. Matching calculations were launched with a frequency step of 25, 5 and 1 Hz. When comparing the results from the calculations with the ones from the measurements many similarities could be found, especially when using a narrower frequency step. Still many of the finer characteristics were lost in the calculations, something that could be caused by a number of things, to mention a few: the numerical truck is defined as completely stiff which is not a satisfactorily approximation of reality, the free field created in the software is to a greater extend more anechoic than the physical room used. The conclusion is that the numerical model offers more of an indication than an answer of how the sound field behaves. Yet these results may be improved if the number of elements is increased and the frequency step diminished, this would however prolong the calculation time. Another possibility is to tune the model even further and not assigning all sections as completely stiff.